In Patent Literature 1, a power supply unit is disclosed which has a configuration that two holder cases incorporating plural power supply modules are stored in an outer case in a state connected to each other by a power supply line, and the power supply modules are cooled by introducing cooling air to the inside of the outer case.
In a case of the power supply unit having the configuration, in order to prevent the cooling efficiency of the power supply module from dropping because the flow of the cooling air is interfered by the power supply line, the power supply line is arranged along and in parallel with the upper surface of the holder case.